High Speed Power Supply System

ABSTRACT

A power supply system includes a high-speed power supply providing a first output, operating in conjunction with an externally supplied DC source or low frequency power supply which provides a second output. A frequency blocking power combiner circuit combines the first and second outputs to generate a third output in order to drive a load, while providing frequency-selective isolation between the first and second outputs. A feedback circuit coupled to the combined, third output compares this combined, third output with a predetermined control signal and generates a control signal for controlling the high-speed power supply, based on a difference between the third output and the predetermined control signal. The feedback circuit does not control the DC source or the low frequency power supply, but controls only the high-speed power supply.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority under 35U.S.C. §120 to U.S. patent application Ser. No. 12/749,260, entitled“High Speed Power Supply System,” filed on Mar. 29, 2010, which claimspriority under 35 U.S.C. §119(e) from U.S. Provisional PatentApplication No. 61/165,377, entitled “High Speed Power Supply System,”filed on Mar. 31, 2009, both of which are incorporated by referenceherein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a high speed power supply system thatcan be used to power an RF PA (Radio Frequency Power Amplifier).

2. Description of the Related Arts

In certain electronic systems, there is a need for a high-speed powersupply to complement an existing DC source or low frequency powersupply. As an illustrative example, a radio system may include an EER(envelope elimination and restoration) transmitter, where the RF PA isfed by a power supply which modulates the PA's power supply voltage orbias, imposing amplitude modulation onto the RF carrier signal.Typically, the power supply feeding such a PA is a linear regulator witha fast response, with the output voltage of the linear regulatorcontrolled electronically to generate the amplitude modulation. Such alinear regulator is inefficient, as linear regulators control the outputvoltage via a dissipative pass transistor. A more efficient alternativecould be to use a switching regulator. Often, in the case of portablebattery-operated electronic devices such as mobile phones, spareswitching regulators already exist within the system. However, theseswitching regulators lack the control bandwidth to modulate their outputvoltage at the rate needed to impose amplitude modulation in many modernradio systems, and therefore are not appropriate as modulators on theirown.

SUMMARY OF THE INVENTION

Embodiments of the present invention include a power supply systemcomprising a high-speed power supply providing a first output, operatingin conjunction with an externally supplied DC source or low frequencypower supply which provides a second output. A frequency blocking powercombiner circuit combines the first and second outputs to generate athird output in order to drive a load, while providingfrequency-selective isolation between the first and second outputs. Afeedback circuit coupled to the combined, third output compares thiscombined, third output with a predetermined control signal and generatesa control signal for controlling the high-speed power supply, based on adifference between the third output and the predetermined controlsignal. The feedback circuit does not control the DC source or the lowfrequency power supply, but controls only the high-speed power supply.The power supply system has the benefit of minimizing cost by harnessingan existing DC source or low frequency power supply to provide asignificant portion of power to the load, while increasing the controlspeed and accuracy of the power supply by adding a high-speed powersupply controlled in a closed-loop manner. The high-speed power supplycan be a push-pull regulator.

The features and advantages described in the specification are not allinclusive and, in particular, many additional features and advantageswill be apparent to one of ordinary skill in the art in view of thedrawings, specification, and claims. Moreover, it should be noted thatthe language used in the specification has been principally selected forreadability and instructional purposes, and may not have been selectedto delineate or circumscribe the inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the embodiments of the present invention can be readilyunderstood by considering the following detailed description inconjunction with the accompanying drawings.

FIG. 1A illustrates a high speed power supply system, according to oneembodiment.

FIG. 1B illustrates additional details of the high speed power supplysystem of

FIG. 1A, according to another embodiment.

FIG. 1C shows additional details of the high speed power supply systemof FIG. 1A, according to still another embodiment.

FIG. 2 illustrates a different variation of the power supply system,according to still another embodiment.

FIG. 3A illustrates a different variation of the power supply system forpowering an RF PA circuit, according to still another embodiment.

FIG. 3B illustrates a different variation of the power supply system ofFIG. 3A for powering an RF PA circuit, according to still anotherembodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

The figures and the following description relate to preferredembodiments of the present invention by way of illustration only. Itshould be noted that from the following discussion, alternativeembodiments of the structures and methods disclosed herein will bereadily recognized as viable alternatives that may be employed withoutdeparting from the principles of the claimed invention.

Reference will now be made in detail to several embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying figures. It is noted that wherever practicable similar orlike reference numbers may be used in the figures and may indicatesimilar or like functionality. The figures depict embodiments of thepresent invention for purposes of illustration only. One skilled in theart will readily recognize from the following description thatalternative embodiments of the structures and methods illustrated hereinmay be employed without departing from the principles of the inventiondescribed herein.

Generally, a power supply system according to the present inventioncomprises a high-speed power supply providing a first output, operatingin conjunction with an externally supplied DC source or low frequencypower supply which provides a second output. A frequency blocking powercombiner circuit combines the first and second outputs to generate athird output in order to drive a load, while providingfrequency-selective isolation between the first and second outputs. Afeedback circuit coupled to the combined, third output compares thisoutput to a predetermined control signal and generates a control signalfor controlling the high-speed power supply, based on a differencebetween the third output and the predetermined control signal. Note thatthe feedback circuit does not control the DC source or the low frequencypower supply and only controls the high-speed power supply. Thehigh-speed power supply can be a push-pull regulator.

The power supply is efficient with sufficient control bandwidth toimpose amplitude modulation in an EER transmitter. The power supplysystem also has the benefit of minimizing cost by harnessing an existingDC source or low frequency power supply (e.g., battery voltage) toprovide a significant portion of power to the load, while increasing thecontrol speed and accuracy of the power supply by adding a high-speedpower supply controlled in a closed-loop manner.

Turning to the figures, FIG. 1A illustrates a high speed power supplysystem 100 according to one embodiment. The high speed power supply 118may be a push-pull regulator in one embodiment. Power 120 from anexternal DC source or low frequency power supply is combined with theoutput power 122 of a high-speed power supply 118 in frequency blockingpower combiner 124 to produce combined output power 126. The lowestfrequency of the frequency range of output power 122 from the high-speedpower supply 118 is at least higher than the lowest frequency of thefrequency range of the DC or lower frequency power source 120. Aconnection 128 provides feedback 130 from output 126 to error amplifier104. The feedback system 102 includes an error amplifier 104 comparingthe feed back signal 130 with control signal 132 to generate powersupply control signal 106. Control signal 132 controls the portion ofthe power supply that is generated by high-speed power supply 118, andmay be generated from a baseband DSP (Digital Signal Processor) in thecase of an EER system for a mobile device such as a cellular telephone.Loop compensation block 109 may be comprised of an electronic networkproviding lead- or lag-phase compensation, gain, or some combinationthereof to ensure overall loop stability. Loop compensation block 109receives power supply control signal 106 and generates such compensatedpower supply control signal 114. DC blocking module 110 prevents DCcomponents from entering feedback system 102 and thus prevents DC levelsfrom limiting the dynamic range of the signal chain fed to thehigh-speed power supply 118. Note that DC blocking module 110 may bemoved to other locations within the circuit 100, replaced by othercircuitry that reduces or eliminates DC components in the feedbacksystem 102, or removed altogether if the design of the feedback system102 and high-speed power supply 118 can tolerate DC components in thesignal path. Feedback system 102 is a negative feedback system. If thefeedback signal 130 is higher than control signal 132, error amplifier104 generates control signal 114 to decrease the output power 122 ofhigh speed power supply 118. On the other hand, if the feedback signal130 is lower than control signal 132, error amplifier 104 generatescontrol signal 114 to increase the output power 122 of high speed powersupply 118. Thus, feedback system 102 forms a negative feedback systemtogether with feedback signal 130.

FIG. 1B shows additional details of the high speed power supply system100 of FIG. 1A, according to one embodiment. The DC blocking module 110may include resistor 161 and capacitor 160 to block DC components ofcontrol signal 132 across the inputs of error amplifier 104. High-speedpower supply 118 may be a push-pull type amplifier 147 with localfeedback 148 to provide fixed gain. The signal 114 which feeds thepush-pull type amplifier 147 may be level-translated (not shown) to a DClevel suitable for the common-mode needs of push-pull type amplifier147. Frequency blocking power combiner 124 may include a capacitor 154coupled in series with the output 122 from high-speed power supply 118,and an inductor 152 coupled in series with the output 120 from theexternally supplied DC source or low frequency power supply. Theinductor 152 passes power at DC or low frequencies, while the capacitor154 passes power at high frequencies and blocks DC and low frequencies.An important aspect of the frequency blocking power combiner network 124is that inductor 152 isolates the high frequency power present atoutputs 126, 122 from entering external source 120. Most DC or lowfrequency sources include large bypassing capacitors (not shown); ifhigh speed power supply 118 were to drive these capacitors at highfrequencies, the high-speed power supply 118 would have to generate highcurrent into and out of these capacitors, resulting in significant powerloss and loss in efficiency. Inductor 152 prevents this from happeningby isolating the high frequency power present at output 126 fromentering external source 120.

FIG. 1C shows additional details of high speed power supply system ofFIG. 1A, according to still another embodiment. The power supply system170 shown in FIG. 1C is substantially the same as the power supplysystem 100 shown in FIG. 1B, except that the frequency blocking powercombiner 127 in this embodiment is comprised of the transformer 160,capacitor 154, and resistor 156. Transformer 160 isolates high frequencypower at the output 122 of high-speed power supply (linear regulator)118 from entering external DC/low frequency power source 120. Thefrequency blocking power combiner 127 also includes a capacitor 154 anda resistor 156 connected in series with the output 122 of the high-speedregulator 147. The capacitor 154 is used to compensate for the leakageinductance at the primary side (nodes 1 and 2) of transformer 160, byresonating this leakage inductance with the capacitor 154. The resistor156 flattens the frequency response created by capacitor 154.

Note that a DC connection exists between the output 122 of high-speedpower supply 118 and ground. Thus, the design of high-speed power supply118 accommodates for this. For example, the output stage of high-speedpower supply 118 may require AC-coupling, or a supply arrangement thatallows a DC common-mode point of 0V.

FIG. 2 illustrates a different variation of the power supply system,according to still another embodiment. The power supply system 200 ofFIG. 2 is substantially the same as the power supply system 100 of FIG.1A, except (i) that the output 126 of the power supply system 200 isused as the supply voltage to an RF PA 204 that receives and amplifiesan RF input signal 208 and generates an RF output signal 210, and (ii)that the RF output signal 210 is sensed 206 and provided to a RFdetector 230 to derive the amplitude signal 130, which in turn is fedback to feedback system 102. RF input signal 208 may be an RF signal fora mobile device to transmit, and thus will be a modulated signalcontaining amplitude modulation information, phase modulationinformation, and/or a combination of both. Thus, external control 132controls the AC portion of the amplitude modulation of PA 204 and its RFoutput signal 210 in a closed-loop manner, while external DC or lowfrequency power source 120 sets the DC or low frequency portion of theamplitude modulation of PA 204 and its RF output signal 210. Inpractice, the voltage at power source 120 may be adjusted to set theaverage power of PA 204, while the amplitude of control signal 132 isset to an appropriate level for this given average power. The control ofpower source 120 and control signal 132 may be set by DACs(digital-to-analog converters, not shown) included in a digital signalprocessor (not shown) which generates the modulation of the RF outputsignal 210. In one embodiment, the power 120 from external DC or lowfrequency power source may be adjusted responsive to the average poweroutput by the power amplifier 104.

FIG. 3A illustrates a different variation of the power supply system forpowering an RF PA circuit, according to still another embodiment.High-speed power supply system 100 is included in a control system 300that is essentially an amplitude correction loop to improve thelinearity of PA 104 and allow the PA 104 to operate into compression,thus efficiently increasing the linear power available from PA 104. Theamplitude correction loop is comprised of various components includingthe amplitude detectors 302, 304, comparator 308, and high-speed powersupply system 100, powering 208 the PA 104. The amplitude correctionloop adjusts the power supply voltage 208 to PA 104 based on anamplitude correction signal 309, which in turn is derived from thedifference in amplitudes between RF input signal 204 and the RF outputsignal 110. RF input signal 204 may be an RF signal for a mobile deviceto transmit, and thus will be a modulated signal containing amplitudemodulation information, phase modulation information, and/or acombination of both. Detectors 302 and 304 determine the amplitudes ofRF input signal 204 and an attenuated version 326 of RF output signal110 (attenuated by attenuator (RFFA) 306), respectively, feedingcomparator 308 with amplitude signals 323 and 322, respectively.Comparator 308 generates an amplitude correction signal 309 based on thedifference or ratio of amplitude signals 323 and 322. The amplitudecorrection signal 309 may connect to control signal 132 in high-speedpower supply system 100 (FIG. 1A), while an external DC or low frequencypower source connects to input 120. The external DC source 120 may be adirect connection to a battery of a mobile device or other electronicdevice, or may be derived from a switching regulator. In one embodiment,the power 120 from external DC or low frequency power source may beadjusted responsive to the average power output by the power amplifier104.

When the RF input signal 204 to PA 104 is relatively low, and PA 104operates substantially below its compression point, comparator 308reports low error in amplitude correction signal 309, and thus thehigh-speed power supply 118 in the high-speed power supply system 100 isessentially inactive, while the external DC or low frequency source 120provides pass-through power to the PA 104. As the RF input signal 204 toPA 104 is increased, the amplitude distortion caused by PA 104 isincreased, and high-speed power supply 118 in the high-speed powersupply system 100 reacts to the error reported in amplitude correctionsignal 309 by comparator 308, by providing a correcting AM modulation tothe power supply 208 of PA 104. Thus, the amplitude error of PA 104 iscorrected in a closed-loop manner. Capacitor 154 (see FIG. 1B) inhigh-speed power supply system 100 charges to the DC (average) voltagebetween combined output 126 and high-speed power supply output 122,allowing the supply voltage 208 supplied to PA 104 to swing above thevoltage supplied by the external DC or low frequency source 120, thusproviding the substantial benefit of a boosted AC supply withoutrequiring a costly boost converter.

Muting block 360, which is optional, has circuitry for providing a meansto reduce or stop the action of the amplitude correction loop when notneeded, thus easing the dynamic range required for the amplitudecorrection loop, and potentially saving quiescent power when the system300 would otherwise be idling. For example, when the amplitude 323 of RFsignals passing through PA 104 is low (detected amplitude 323 is low,for example, lower than a predetermined threshold), muting block 360 mayreduce or mute the output 309 of comparator 308 by use of a mute controlsignal 342, and/or shut down the high-speed power supply 118 within thehigh-speed power supply system 100 by use of a shut-down control signal344. Alternatively, the distortion 340 of RF output signal 110 may bedetermined by an independent means (for example, error-vector magnitudeevaluated by a DSP, not shown), and the muting block 360 may similarlyreduce the action of the amplitude correction loop when a low value ofdistortion 360 is detected in the RF output signal 110 (for example,when the distortion 360 is lower than a predetermined threshold). In yetanother example, the voltage of the external DC or low frequency powersource 120 may be measured to detect whether it is high enough to affordPA 104 sufficient voltage headroom without need for correction, in whichcase the action of the amplitude correction loop may be reducedsimilarly. Any of these methods may be used independently or inconjunction with each other as a means to stop or reduce the action ofthe amplitude correction loop when not needed.

FIG. 3B illustrates a different variation of the power supply system ofFIG. 3A for power an RF PA circuit, according to still anotherembodiment. The power supply system 350 of FIG. 3B is substantially thesame as the power supply system 300 described in FIG. 3A, except that aVGA (Variable Gain Amplifier) 502 and a phase control loop have beenadded to the signal path of PA 104. VGA 502 provides the ability for theamplitude correction loop to additionally correct the RF input amplitudeto the PA 104, easing the bandwidth requirements of high-speed powersupply system 100. Gain control block 506 apportions at least higherfrequency portions 504 of amplitude correction signal 309 to adjust thegain of VGA 502, and also generates the amplitude correction signal 509to high-speed power supply system 100 as its power control signal 132.Phase shifter 320, together with limiters 312, 314, phase detector 316and phase loop filter (PLF) 318, provide the phase control loop tocorrect AM-to-PM (amplitude modulation to phase modulation) distortioncreated by PA 104. The RF input signal 204 and attenuated output signal326 are limited to remove amplitude information by limiters 312 and 314,to produce limited signals 324 and 325, respectively. Phase detector 316compares the phase of limited signal 324 with the phase of limitedsignal 325, and the resulting phase difference 317 is passed throughphase loop filter 318 to generate phase control signal 319. Phasecontrol signal 319 controls phase shifter 320 in a closed-loop fashionto maintain a fixed phase difference between the RF input signal 204 andthe RF output signal 110.

Upon reading this disclosure, those of skill in the art will appreciatestill additional alternative designs for a high speed power supplysystem. Thus, while particular embodiments and applications of thepresent invention have been illustrated and described, it is to beunderstood that the invention is not limited to the precise constructionand components disclosed herein and that various modifications, changesand variations which will be apparent to those skilled in the art may bemade in the arrangement, operation and details of the method andapparatus of the present invention disclosed herein without departingfrom the spirit and scope of the present invention.

What is claimed is:
 1. A power supply system, comprising: a power sourceconfigured to generate first output power in a first frequency range; apower supply configured to generate second output power in a secondfrequency range, a lower end of the second frequency range being atleast higher than a lower end of the first frequency range; a powercombiner circuit configured to combine the first output power with thesecond output power to generate a combined output power; and a feedbackcircuit coupled to receive a feedback signal indicative of the combinedoutput power through a feedback loop, the feedback circuit configured tocompare the feedback signal with a control signal and generate a powersupply control signal for controlling the power supply based on adifference between the feedback signal and the control signal, andwherein the power source is not controlled based on the differencebetween the feedback signal and the control signal.
 2. The power supplysystem of claim 1, wherein the power source is a DC (direct current)power source.
 3. The power supply system of claim 1, wherein the powersource is another power supply configured to generate the first outputpower in the first frequency range.
 4. The power supply system of claim1, wherein the power supply is a push-pull regulator.
 5. The powersupply system of claim 1, wherein the feedback circuit includes an erroramplifier configured to compare the feedback signal with the controlsignal to generate the power supply control signal.
 6. The power supplysystem of claim 5, further comprising a loop compensation circuitcoupled in series between the error amplifier and the power supply, theloop compensation circuit configured to provide phase compensation orgain compensation to the power supply control signal.
 7. The powersupply system of claim 1, further comprising a DC blocking circuitcoupled in series with the control signal, the DC blocking circuitconfigured to block DC components of the control signal from enteringthe feedback circuit.
 8. The power supply system of claim 7, wherein theDC blocking circuit comprises a capacitor coupled in series with thecontrol signal.
 9. The power supply system of claim 1, wherein the powercombiner circuit includes an inductor coupled in series with the firstoutput power from the power source.
 10. The power supply system of claim1, wherein the power combiner circuit includes a capacitor coupled inseries with the second output power from the power supply.
 11. The powersupply system of claim 1, wherein the power combiner circuit includes atransformer including a primary winding with a first node and a secondnode and a secondary winding with a third node and a fourth node, thefirst node coupled to receive the first output power, the second nodecoupled to a load, the third node coupled to ground, and the fourth nodecoupled to receive the second output power.
 12. The power supply systemof claim 11, wherein the power combiner circuit further includes acapacitor coupled to the power supply and the fourth node of thetransformer on one end and the load on another end, the capacitorreducing effects of a primary leakage inductance of the transformer. 13.The power supply system of claim 12, wherein the power combiner circuitfurther includes a resistor coupled in series between the capacitor andthe load, the resistance flattening a frequency response created by thecapacitor.
 14. The power supply system of claim 1, wherein the powersupply control signal is configured to decrease the second output powerfrom the power supply if the feedback signal is higher than the controlsignal, and increase the second output power from the power supply ifthe feedback signal is lower than the control signal.
 15. The powersupply system of claim 1, further comprising: a RF power amplifierconfigured to receive and amplify a RF input signal to generate a RFoutput signal under control of the combined output power.
 16. The powersupply system of claim 1, further comprising : circuitry configured togenerate the control signal based on an amplitude of the RF inputsignal.
 17. A power supply system for providing power to a radiofrequency (RF) power amplifier, comprising: a power source configured togenerate first output power in a first frequency range; a power supplyconfigured to generate second output power in a second frequency range,a lower end of the second frequency range being at least higher than alower end of the first frequency range; a power combiner circuitconfigured to combine the first output power with the second outputpower to generate combined output power for providing power to the RFpower amplifier, the RF power amplifier receiving and amplifying a RFinput signal to generate a RF output signal under control of thecombined output power; and a feedback circuit coupled to receive afeedback signal indicative of an amplitude of the RF output signalthrough a feedback loop, the feedback circuit configured to compare thefeedback signal with a control signal and generate a power supplycontrol signal for controlling the power supply based on a differencebetween the feedback signal and the control signal, and wherein thepower source is not controlled based on the difference between thefeedback signal and the control signal.
 18. The power supply system ofclaim 17, further comprising a DC blocking circuit coupled in serieswith the control signal, the DC blocking circuit configured to block DCcomponents of the control signal from entering the feedback circuit. 19.The power supply system of claim 17, wherein the power combiner circuitincludes an inductor coupled in series with the first output power fromthe power source.
 20. The power supply system of claim 17, wherein thepower combiner circuit includes a capacitor coupled in series with thesecond output power from the power supply.
 21. The power supply systemof claim 17, wherein the power combiner circuit includes a transformerincluding a primary winding with a first node and a second node and asecondary winding with a third node and a fourth node, the first nodecoupled to receive the first output power, the second node coupled to aload, the third node coupled to ground, and the fourth node coupled toreceive the second output power.
 22. The power supply system of claim17, wherein the power supply control signal is configured to decreasethe second output power from the power supply if the feedback signal ishigher than the control signal, and increase the second output powerfrom the power supply if the feedback signal is lower than the controlsignal.
 23. The power supply system of claim 17, wherein the firstoutput power from the power source is adjusted responsive to an averagepower output by the RF power amplifier.
 24. A power amplifier controllercircuit for controlling a power amplifier, the power amplifier coupledto receive and amplify a radio frequency (RF) input signal to generatean RF output signal, the power amplifier controller circuit comprising:an amplitude control loop configured to determine an amplitudecorrection signal indicative of an amplitude difference between anamplitude of the input signal to the power amplifier and an attenuatedamplitude of the output signal of the power amplifier; and a powersupply system including: a power source configured to generate firstoutput power in a first frequency range; a power supply configured togenerate second output power in a second frequency range, a lower end ofthe second frequency range being at least higher than a lower end of thefirst frequency range; a power combiner circuit configured to combinethe first output power with the second output power to generate combinedoutput power, the combined output power providing power to the poweramplifier; and a feedback circuit coupled to receive a feedback signalindicative of the combined output power through a feedback loop, thefeedback circuit configured to compare the feedback signal with theamplitude correction signal and generate a power supply control signalfor controlling the power supply based on a difference between thefeedback signal and the amplitude correction signal, and wherein thepower source is not controlled based on the difference between thefeedback signal and the amplitude correction signal.
 25. The poweramplifier controller circuit of claim 24, wherein the first output powerfrom the power source is adjusted responsive to an average power outputby the power amplifier.
 26. The power amplifier controller circuit ofclaim 24, further comprising a muting circuit configured to reduce ormute the amplitude correction signal responsive to the amplitude of theRF input signal being lower than a threshold.
 27. The power amplifiercontroller circuit of claim 24, further comprising a muting circuitconfigured to shut down the power supply system responsive to theamplitude of the RF input signal being lower than a predeterminedthreshold.
 28. The power amplifier controller circuit of claim 24,further comprising a muting circuit configured to reduce the amplitudecorrection signal responsive to distortion in the RF output signal beinglower than a predetermined threshold.
 29. The power amplifier controllercircuit of claim 24, wherein the amplitude control loop includes avariable gain amplifier configured to adjust the amplitude of the RFinput signal to the power amplifier based upon a gain control signalderived from the amplitude correction signal.
 30. The power amplifiercontroller circuit of claim 24, further comprising a phase control loopconfigured to determine a phase error signal indicative of a phasedifference between phases of the RF input signal to the power amplifierand the RF output signal of the power amplifier and adjust the phase ofthe RF input signal to the power amplifier to reduce phase distortiongenerated by the power amplifier.